For cosmetic purposes, contact lenses having one or more colorants dispersed in the lens or printed on the lens are in high demand. These colored contact lenses enhance the natural beauty of the eye, or provide unique patterns on the iris of the wearer, or provide non cosmetic patterns or marks, such as rotation marks, inversion marks, product/brand codes, lot numbers, “DEMO” lenses, and the like, which are of benefits to wearers, eye-care practitioners and manufacturers. Various methods have been disclosed to make printing inks suitable for printing either hydrophilic (hydrogel) contact lenses or the molds that are then used to make hydrogel contact lenses.
U.S. Pat. No. 4,668,240 to Loshaek discloses colored contact lenses produced with a lens polymer that contains one or more of the functional groups —COOH, —OH, or —NH—R, wherein R is hydrogen or C1 to C8 alkyl. At least a portion of the surface of the lens is coated with a color coat comprising at least one pigment, binder polymer having the same functional groups, and an additional compound having at least two groups per molecule selected from at least one of —NCO and epoxy. The Loshaek patent discloses also that the lens polymer may contain one or more of the functional groups —NCO or epoxy whereas the binder polymer may contain one or more of the functional groups —COOH, —OH, or —NH—R. The lens and binding polymers are then bound to each other by the reaction of the groups —COOH, —OH, or —NH—R in the lens or the binder polymer and binding polymers with the groups —NCO or epoxy in the binder polymer or the lens.
U.S. Pat. No. 4,857,072 to Narducy, et al. discloses a method for making colored hydrophilic contact lenses. At least a portion of the surface of the lens is coated with a color coat comprising at least one pigment, binding polymer having functional groups, and an additional compound having at least two groups per molecule of —NCO. The coated lens is then subjected to conditions that cause the color coat to adhere to the lens.
U.S. Pat. No. 5,272,010 to Quinn discloses a method for preparation of colored contact lenses similar to that of U.S. Pat. Nos. 4,668,240 and 4,857,072 except that an isocyanate compound is not required. Instead, adhesion promoters such as hexamethoxymethylmelamine are used.
U.S. Patent Application publication No. 2003/0054109 to Quinn, et al. discloses a method for making colored hydrophilic contact lenses. At least a portion of a surface of a lens is coated with a color coat comprising at least one colorant, and a binder polymer having latent crosslinkable pendent groups (e.g., epoxy, hydroxy, alkenyl, isocyanate, peroxy, perester, anhydride, silane, and combinations thereof). The lens is then subjected to conditions that cause the color coat to adhere to the lens. In such method, inks are substantially free of a separate adhesion promoter species such as hexamethylene diisocyanate or hexamethoxymethylmelamine.
However, the methods known in the art have several disadvantages. First, inks described in the prior art are for non-silicone hydrogel lenses and would be undesirable for use with silicone hydrogels. In recent years, silicone hydrogel contact lenses, for example, Focus NIGHT & DAY™ (CIBA VISION), become more and more popular because of corneal health benefits provided by their high oxygen permeability and comfort. Inks described in the prior art have properties (e.g., surface energy, oxygen permeability, water content, expansion characteristics, etc.) which may not be compatible with silicone hydrogel lenses, since they are designed for conventional (non-silicone) hydrogels and not for silicone hydrogel lenses. They may have adverse effects to the properties of silicone-hydrogel lenses.
Second, inks described in the prior art may have issues of instability because of reactive functional groups present in adhesion promoter, activators (activating agent or agents), and binder polymers in the inks. Premature reactions may occur between the reactive functional groups, having a negative impact on print quality, ink pot life, and lens adhesion ability of the ink.
Third, inks described in the prior art may need to have an additional agent or a reactive coating to be added during the manufacturing process to promote adhesion of the color coat to a lens. This has all the disadvantages associated with adding an additional ingredient to a manufacturing process.
Fourth, inks described in the prior art may not provide a manufacturer flexibility for curing (gelling) inks or promoting lens adhesion of a color coat. For example, thermal curing is often performed after printing an ink on one of the molding surfaces of a plastic (e.g., polypropylene) disposable mold. Thermally curing of an ink on a plastic disposable mold prior to lens fabrication might distort the mold and result in a lens of unacceptable quality. In addition, thermal curing of an ink might result in thermal oxidative processes involving polypropylene mold surfaces. As such, thermal curing may negatively affect on cure kinetics and lens quality.
Therefore, there exist needs for methods of making colored silicone hydrogel contact lenses, and for inks suitable for printing a high-quality color image on a silicone hydrogel contact lens.